The work done by a force is the product of the force, the displacement and the cosine of the angle between them.
Symbols
W
work
[J]
F
force
[N]
s
displacement
[m]
α
angle between the force and the displacement
[°]
Where it comes from
Work depends on the component of the force along the displacement. A force perpendicular to the motion (cos90∘=0) does no work (e.g. the centripetal force). A force in the direction of motion does positive work; one opposing it does negative work.
When to use it
Calculating the work done by a constant force. When the force acts along the motion, α=0 and W=Fs.
Example
A 50 N force pulls a crate 4 m at an angle of 60° to the direction of motion. Find the work done.